1. Field of the Invention
The present invention relates to a speaker system, and more particularly relates to a speaker system which is capable of expanding a cabinet capacity by using a gas adsorbent made from a porous material and which is capable of improving performance in a bass sound reproduction.
2. Description of the Background Art
In a conventional speaker system, due to an effect of an acoustic stiffness caused by an internal cavity of a cabinet, it has been difficult to realize a speaker system which is small and which is capable of reproducing a bass sound. As a solution to solve limits of the bass sound reproduction, which are determined by the capacity of the internal cavity of the cabinet, a speaker system which has an aggregate of activated carbon situated inside the cabinet has been suggested (e.g., Japanese National Phase PCT Laid-Open Publication No. 60-500645). FIG. 34 is a tectonic profile of a conventional speaker system disclosed in Japanese National Phase PCT Laid-Open Publication No. 60-500645.
As shown in FIG. 34, the conventional speaker system includes a cabinet 1, a speaker unit 2, a gas adsorbent 3, a supporting material 4, a diaphragm 5 and a bent tube 6. The speaker unit 2 is fixed to the cabinet 1. The gas adsorbent 3 is made from a porous material which is capable of adsorbing/desorbing air molecules, and is situated inside the cabinet 1. In FIG. 34, the gas adsorbent 3 is composed by aggregating granular activated carbon, which is the porous material. The supporting material 4 is provided inside the cabinet 1 so as to support the gas adsorbent 3. The entire surface of the supporting material 4 has pores formed thereon so as to allow the air to pass through. The diaphragm 5 is provided inside the cabinet 1 so as to divide the internal cavity of the cabinet 1 into R1 and R2. The bent tube 6 is fixed to the diaphragm 5 so as to allow ventilation between the internal cavity R1 and the internal cavity R2.
An operation of the speaker system configured as above will be described. When an acoustic signal is applied to the speaker unit 2, the diaphragm of the speaker unit 2 vibrates, and an air pressure of the internal cavity R1 changes. Due to this change in the air pressure, the diaphragm 5 vibrates. The supporting material 4 has pores on the entire surface thereof, and thus the air pressure of the entire internal cavity R2 changes due to the vibration of the diaphragm 5. The gas adsorbent 3 adsorbs/desorbs ambient air molecules in accordance with the change in the air pressure of the internal cavity R2. Due to the adsorption/desorption action, the change in the air pressure of the internal cavity R2 is reduced, and the change in the air pressure of the internal cavity R1 is also reduced. In this manner, the change in the air pressure of the entire internal cavity of the cabinet 1 is reduced, and accordingly the cabinet 1 operates as if having a large capacity in an equivalent manner. Accordingly, the conventional speaker system, which has a small cabinet, has been capable of operating as if a speaker unit is fixed to a cabinet having a large capacity, and also capable of realizing a bass sound reproduction.
However, moisture outside the cabinet 1 flows inside the cabinet through the diaphragm and an edge of the speaker unit. When an ambient humidity is high, the gas adsorbent 3 adsorbs moisture in the air, and consequently, the adsorption/desorption action of the gas adsorbent 3 deteriorates. Therefore, a cabinet capacity expansion effect, as above described, decreases. Accordingly, in Japanese National Phase PCT Laid-Open Publication No. 60-500645, the diaphragm 5 is provided so as to prevent the moisture from flowing into the internal cavity R2 from the outside of the cabinet 1.
However, when a temperature around the speaker system increases, or when an atmospheric pressure around the speaker system decreases, the air confined in the internal cavity R2 inflates, and the air molecules adsorbed by the gas adsorbent 3 are discharged therefrom. Therefore, when the internal cavity R2 is completely sealed by the diaphragm 5, the diaphragm 5 is displaced toward a front side of the speaker system. When the diaphragm 5 is displaced toward the front side of the speaker system, the vibration of the diaphragm 5 is disturbed, and the cabinet capacity expansion effect caused by the gas adsorbent 3 decreases. Further, the diaphragm 5 is likely to be broken. The problem like this may also occur when the temperature around the speaker system decreases or when an atmospheric pressure around the speaker system increases.
Therefore, in Japanese National Phase PCT Laid-Open Publication No. 60-500645, the bent tube 6 is provided to the diaphragm 5. When the air in the internal cavity R2 inflates/deflates, the air moves inside the bent tube 6 in accordance with the inflation/deflation. Accordingly, since an increase/decrease in the air in the internal cavity R2 is suppressed, it is possible to prevent the decrease in the cabinet capacity expansion effect caused by the gas adsorbent 3 and also possible to prevent breaking of the diaphragm 5.
Further, in Japanese National Phase PCT Laid-Open Publication No. 60-500645, powdery activated carbon (not shown) of 0.05 mm diameter is filled in the bent tube 6. The powdery activated carbon is filled in order to prevent the air from flowing through the bent tube 6 in a frequency band in which the speaker unit 2 operates, and also to minimize moisture flowing into the internal cavity R2 from the outside of the cabinet 1.
However, it is generally difficult to handle the powdery activated carbon which is filled in the bent tube 6, since fluidity of the powdery activated carbon needs to be maintained, and since the powdery activated carbon tends to cause static electricity. It is also extremely difficult to stably fill the powdery activated carbon into a narrow tube such as the bent tube 6. Disclosed in Japanese National Phase PCT Laid-Open Publication No. 60-500645 is that the powdery activated carbon having a diameter of 0.05 [mm] is filled in the bent tube 6 having a diameter of 8 [mm] and a length of about 60 [cm]. However, it is extremely difficult to realize the situation. In other words, it is substantially impossible for the conventional speaker system disclosed in the Japanese National Phase PCT Laid-Open Publication No. 60-500645 to minimize the moisture flowing into the internal cavity R2 from the outside of the cabinet 1.